This is a continuation application of International Patent Application PCT/CH01/00095, filed on Feb. 13, 2001, which claims priority to German Patent Application No. DE 100 08 825 A1, filed on Feb. 25, 2000, both of which are incorporated by reference herein.
The invention relates to a micro perfusion device for obtaining at least one constituent of a body fluid by means of a subcutaneously positioned perfusion catheter.
FIG. 7D shows a micro perfusion device as described in xe2x80x9cOpen-Flow Microperfusion . . . xe2x80x9d, Z. Trajanoski et al., Diabetes Care, Volume 20, Number 7, July 1997, pages 1114 ff. The device comprises a casing 1 which may be fixed to the skin. A flexible, permeable perfusion catheter 5a projects from the casing 1, said catheter being subcutaneously positioned in a tissue 3. A supply catheter 7a for a rinsing liquidxe2x80x94referred to as perfusate in the following protrudes into the perfusion catheter 5a. The perfusion catheter 5a and the supply catheter 7a form a double-lumen catheter in the tissue 3, comprising an inner lumen within the supply catheter 7a and a surrounding outer lumen between the supply catheter 7a and the perfusion catheter 5a. In the casing 1, the outer lumen feeds into a discharge channel 8 to which a discharge catheter is connected. In order to obtain body fluid from the tissue 3, the perfusate is guided through the supply catheter 7a up close to a front distal end of the perfusion catheter 5a. Once the perfusate has emerged at the front distal of the supply catheter 7a, it flows back along the supply catheter 7a in the outer lumen. A rinsing liquid is used as the perfusate which penetrates the constituent whose concentration in the body fluid is to be ascertained. Furthermore, body fluid is sucked into the outer lumen through the perforated perfusion catheter 5a by the rinsing effect. The mixture of perfusate and body fluid is discharged through the discharge channel 8 to a measuring means. The fluid is conveyed through the device by means of a pump.
The placement procedure prior to the use of the perfusate can be seen from FIGS. 7A to 7D. An injection needle 4a is used to position the device. Before it is positioned, the perfusion catheter 5a tightly surrounds the injection needle 4a. Once the skin has been pierced and the injection needle 4a positioned in the tissue 3 (FIG. 7A), the injection needle 4a is retracted again (FIG. 7B), and the perfusion catheter Sa remains in the tissue in the position shown. The supply catheter 7a is then inserted through the casing 1 into the perfusion catheter 5a (FIG. 7C). It is inserted in the perfusion catheter 5a until it takes up most of the length of the perfusion catheter 5a (FIG. 7D). The front end of the supply catheter 7a is, however, some distance short of the front end of the perfusion catheter 5a. 
Micro perfusion devices of the type described require piercing the skin, retracting the injection needle and subsequently providing a perfusate supply.
It is therefore an object of the invention to provide a micro perfusion device which can be easily positioned and operated.
The present invention, in one embodiment, is a micro perfusion device for obtaining at least one constituent of a body fluid using a subcutaneously positioned perfusion catheter comprising a casing, a supply for a perfusate, a hollow injection needle, the perfusion catheter and a discharge channel formed in the casing for discharging the perfusate together with the at least one constituent. The injection needle comprises a front needle opening, distal when subcutaneously positioned, and a rear needle opening. The front needle opening can be formed by a front-facing opening in the conventional way, for example by needle grinding. It can also be formed by a lateral opening in a surface of the injection needle. In one embodiment, the rear needle opening is formed on the rear facing side of the injection needle. It can be formed by a slit or a bore or by laterally cutting the surface area of the injection needle. The injection needle is accommodated by the casing, and may be slid from a front sliding position to a rear sliding position. In its front sliding position, it protrudes through the perfusion catheter. In its rear position, it protrudes into the perfusion catheter, however the perfusion catheter protrudes beyond its front needle opening in the rear position. The injection needle can be a steel needle. Alternatively, other needles can be used as long as they have a sharp tip to cleanly penetrate the skin, are sufficiently rigid for positioning, and are histocompatible.
The injection needle in one aspect of the invention serves to position the perfusion catheter in a tissue whose body fluid and/or from its body fluid the at least one constituent is to be obtained. Alternatively, the injection needle not only fulfills the function of positioning the perfusion catheter, but also fulfills the further function of introducing the perfusate into the perfusion catheter. To this end, a fluid connection from the perfusate supply into the injection needle is formed by the rear needle opening, at least in the rear sliding position of the injection needle. When the device is implanted, i.e. subcutaneously positioned, the perfusate is thus introduced through the perfusate supply, the rear needle opening, the hollow injection needle and finally through its front needle opening into the surrounding perfusion catheter and then rinses the perfusion catheter. Since the injection needle assumes the double function of positioning and introducing the perfusate, the step of subsequently inserting a perfusate supply into the perfusion catheter can be omitted.
According to one embodiment of the present invention, the micro perfusion device can be formed by simply developing catheter heads such as those for infusing insulin within the framework of diabetotherapy. A particularly suitable catheter head is described in DE 198 21 723.4 by the Applicant. The catheter head described therein already comprises an injection needle accommodated slidably in the catheter head casing, with a front and a rear needle opening. The rear needle opening is formed by a lateral opening through which, once an infusion catheter has been positioned, the insulin solution is supplied for the purpose of priming the catheter head. With respect to the injection needle of this catheter head, only a fluid-proof connection is required in the area of the rear needle opening for supplying the perfusate. Furthermore, a discharge channel having a fluid-proof connection to the infusion catheter or perfusion catheter, respectively, has to be formed in the catheter head. As a perfusion catheter, the infusion catheter can be perforated.
The micro perfusion device, in one embodiment, serves to measure or ascertain the glucose concentration in the body fluid in the vicinity of the implanted perfusion catheter. In this case, the at least one constituent of the body fluid is glucose. The body fluid together with the perfusate can be obtained quite simply by the rinsing process. By using an appropriate perfusate or rinsing fluid, a particular constituent can also be selectively obtained by means of the micro perfusion device in accordance with the invention, in addition to the body fluid rinsed with it.
Perfusion, according to one aspect of the present invention, is achieved by suctioning the discharge channel by means of a pump. The perfusate can also be pressed into the injection needle. Alternatively, it can be conveyed by a combination of pressure and suction.
In one embodiment, the fluid connection between the perfusate supply and the injection needle only exists in the rear sliding position of the injection needle. In this case, the perfusate supply is a supply channel formed in the casing. In the rear sliding position, the injection needle opens into this supply channel via its rear needle opening. This ensures that the perfusate discharge in the casing is sealed fluid-proof with respect to the perfusion supply. Appropriate sealing means can be provided in the casing for this purpose.
In another embodiment, the rear needle opening of the injection needle is permanently connected to the perfusate supply. For this purpose, a catheter forming the perfusate supply can very simply be placed over the rear end of the injection needle, which is open-back on its facing side, or otherwise connected fluid-proof to the inner hollow space of the injection needle.
The perfusion catheter can be formed by a catheter closed on its surface side, having only an open front facing side. Alternatively, the perfusion catheter is laterally permeable to the constituent to be measured or, selectively, only for the constituent to be measured or for the body fluid as a whole. The to perfusion catheter can be manufactured from a porous material. If the perfusion catheter is perforated, then the lateral perforation openings of the perfusion catheter can be elongated in the longitudinal direction of the catheter, in order to obtain as great a stability against straining as possible. Straining the catheter as it is inserted into the tissue, also known as peal back effect, is thus prevented or at least kept to a minimum. The perforation openings can be arranged on gaps or offset with respect to each other, not along a line extending in the longitudinal direction of the perfusion catheter but in the circumferential direction of the perfusion catheter. The catheter can be perforated as it is formed, or subsequently, for example using lasers.
In order to obtain a perfusion catheter which is as slim as possible, the outer cross-section of the injection needle and the inner cross-section of the perfusion catheter exhibit different shapes, such that the perfusion catheter only abuts the injection needle in longitudinal strips, and a longitudinal gap remains between adjacent longitudinal strips. In one embodiment, either the injection needle or the perfusion catheter exhibits a cross-section which deviates from the circular form. In this form, the perfusion catheter can wrap tightly around the injection needle along its entire length situated in the tissue. A flow cross-section for the perfusate flowing back nonetheless remains between the outer surface area of the injection needle and the inner surface area of the perfusion catheter. If, for example, the injection needle exhibits an outer cross-section deviating from the circular form along its implanted length, then the perfusion catheter can exhibit a circular inner cross-section tensed around the needle. Equally, the perfusion catheter can exhibit a non-circular inner cross-section and the injection needle a circular outer cross-section. However, it is also possible for the outer cross-section of the injection needle and the inner cross-section of the perfusion catheter to deviate from the circular form, so long as it is ensured that a sufficient flow cross-section for the purpose of rinsing remains between the needle and the perfusion catheter and that the perfusion catheter surrounds the injection needle, in some embodiments the perfusion catheter being wrapped tightly around the injection needle, for the purpose of securely implanting it.
In its rear sliding position, the injection needle is, according to one aspect of the invention, fixed to the casing in such a way that it can be tactilely sensed by someone using the micro perfusion device when the injection needle is in its rear sliding position. The injection needle can simply be moved into its rear sliding position against a stopper. The injection needle can be fixed not only against sliding further, beyond the rear sliding position, but also against the injection needle advancing. The injection needle can be fixed to the casing in its rear sliding position by means of a locking connection, such as a detachable locking connection. For fixing the injection needle, a protrusion, a dent, a slit or the like can be formed on the injection needle. In one embodiment, the rear needle opening is used for the purpose of the locking connection.
In a further embodiment, the micro perfusion device is not only used to obtain the at least one constituent of the body fluid, but simultaneously serves as a miniature measuring means or at least as an electrode platform for a measuring means. The measuring means can serve to measure or ascertain the concentration of the at least one constituent in the body fluid. When used as an electrode platform, an electrode of the measuring means is formed on the lower side of the casing, via which the casing sits on the tissue. A working electrode of the measuring means is electrically connected to the discharged rinsing fluid and can be arranged in the discharge channel of the casing. The electrode formed on the lower side of the casing forms the counter electrode to this working electrode and serves to measure an electrical current and/or an electrical potential. In one aspect of the present invention, a sufficiently large bearing area is formed on the lower side of the casing for the counter electrode to be able to form a sufficiently large contact area with the tissue and simultaneously be used as a reference electrode. Furthermore, it can fulfill an adhesive function, for adhering to the skin.
When it is formed as a miniature measuring means, a sensor is arranged in the casing of the micro perfusion device, the sensor in one aspect of the invention measuring the concentration of the at least one constituent in the body fluid. More precisely, the concentration in the perfusate flowing back is measured and from this, the concentration in the body fluid are ascertained. The sensor can be arranged in an area of the outlet bordering the outer lumen. It can be inserted or recessed into a side wall of the outlet and, in one embodiment, does not protrude out of the wall, in order to keep the flow resistance to a minimum. According to another aspect of the invention, no parts of the casing wall or only as much casing wall as is necessary to securely attach the sensor is arranged in the flow path between the outer lumen and the sensor. The sensor is thus arranged as near to the sampling point as possible, but outside the body.
Although forming it with an integrated sensor, as an electrode platform and as an electrode platform with an integrated sensor are particularly advantageous in combination with the micro perfusion device in accordance with the invention, each of these formations, in particular forming an electrode on the lower side of the casing, can also be realized with all conventional micro perfusion devices.